1. Technical Field
The present invention relates to a lens driving apparatus that drives a lens.
The contents of the following Japanese patent application(s) are incorporated herein by reference:                NO. 2015-036401 filed on Feb. 26, 2015.        
The contents of the following Japanese utility model application(s) are incorporated herein by reference:                NO. 2015-003917 filed on Aug. 1, 2015.        
2. Related Art
A camera installed in a mobile phone or the like is provided with a lens driving apparatus that drives an optical element such as a lens to be used for image-capturing for purposes of focusing or zooming. Many lens driving apparatuses comprise a bobbin that holds an optical element, a cover that houses the bobbin therein, and a drive unit that moves the bobbin in the optical axis-direction of the lens.
When the bobbin is moved by the drive unit, a portion of the bobbin to which the drive unit is provided is moved by a predetermined distance. On the other hand, in some cases, the other portions are moved by distances that are not equal to the moving distance of the portion to which the drive unit is provided due to the gravitational force that acts in the opposite direction to the driving direction or the like, and the orientation of the bobbin inclines, which causes misalignment of the optical axis-direction of the lens. As a measure to solve this, a support unit that supports the bobbin to stabilize the orientation of the bobbin (the optical axis-direction of the lens) and guide the bobbin in the optical axis-direction is provided.
As such a support unit, one in which grooves facing each other are provided to the bobbin and the cover, and a spherical ball is arranged therein has been widely used. This is for suppressing the influence of a frictional force generated in the support unit when moving the bobbin, by the ball rotating while being in contact with the bobbin and the cover.
Conventionally, a drive unit is provided along one surface of a polygonal cylindrical bobbin having a rectangular section, and a support unit is provided along a surface facing the drive unit (please see Patent Literatures 1 and 2, for example). That is, the drive unit and the support unit are arranged in parallel. For this reason, for example, when the drive unit moves the bobbin upward, and the gravitational force that acts in the opposite direction to the moving direction acts on the support unit-side, it is difficult to move a surface of the bobbin to which the support unit is provided by a distance equal to the moving distance of a surface to which the drive unit is provided against the gravitational force, resulting in inclination of the bobbin relative to the cover, that is, to the optical axis.
Also, in order to drive the bobbin smoothly in the optical axis-direction, it is preferable to increase the driving force for example by increasing the size of a drive magnet to increase the magnetic force of the drive magnet.
However, for example if the magnetic force of the drive magnet is increased, the frictional force between a ball arranged between a bobbin and a cover, and the bobbin and the cover increases due to the magnetic attraction force between the drive magnet and the cover. For this reason, situations have occurred where the bobbin is not driven smoothly in the optical axis-direction even if the magnetic force of the drive magnet is increased.